package com.wuhongyu.stackAndqueue;

public class LoopQueue<E> implements Queue<E>{
    private E[] data;
    private int size;
    //循环队列的头,尾
    private int head,tail;

    public LoopQueue(int capacity) {
        data = (E[])new Object[capacity+1];
    }

    public LoopQueue() {
        this(10);
    }

    int getCapacity(){
        return data.length-1;
    }

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return size==0;
    }


    //入队
    @Override
    public void enqueue(E e) {
        if(size==data.length-1){
            resize(getCapacity()*2);
        }
        data[tail] = e;
        //维护一下尾
        tail = (tail+1)%data.length;
        size++;
    }

    private void resize(int capacity) {
        E[] newdata = (E[])new Object[capacity+1];
        for(int i=0; i<size; i++){
            newdata[i] = data[(head+i)%data.length];
        }
        data = newdata;
        head=0;
        tail=size;
    }

    //出队
    @Override
    public E dequeue() {
        if(isEmpty()){
            throw new IllegalArgumentException("队列为空");
        }
        E e = data[head];
        data[head] = null;
        //维护头
        head = (head+1)%data.length;
        size--;
        if(size==getCapacity()/4 && getCapacity()/2!=0){
            resize(getCapacity()/2);
        }
        return e;
    }

    @Override
    public E getFront() {
        if(isEmpty()){
            throw new IllegalArgumentException("队列为空");
        }
        return data[head];
    }


}